2. Carry-on baggage should be small enough to fit under the seat or overhead bin. In the event that the sum of the three dimensions of baggage exceeds 115 centimeters and/or the weight is more than 10 kilograms, the piece of baggage will not be allowed as free baggage. If size, weight or number of baggage is excessive, it is considered as a checked baggage.

3. Wheel chair used for the disabled himself is considered as a checked bagged.

4. As for an infant or child paid with discounted amount by 5,000KRW from adult fare, the same provisions of the Clause 1 and 2, and Article 28 apply.

5. Infant defined in Clause 1 of Article 14 of these conditions is not applied with the provision of Clause 4 of this Article and Article 28. However, either foldable stroller, baby carriage or baby car seat can be used as a free checked baggage.

Answering the question for web check in:

Please read the Article 19 below.

It means you need to check in at the counter based on my understanding.